Generally, various irradiation methods of transmitting a proton beam generated by an accelerator such as a cyclotron or a synchrotron to a patient for radiotherapy using protons have been used. One of general proton beam transmission methods which are currently being used most in proton-therapeutic institutions is a scattering mode in which a large therapeutic irradiation surface is formed by allowing protons to collide with a target of a certain material to be scattered.
Meanwhile, when a flux of a therapeutic proton beam source is incident on a patient, an absorbed dose changes according to depth. Since the change depends on many conditions such as energy and the depth of the flux, a distance from the beam source, etc., a dose of the patient may be calculated considering variations which have an effect on a dose distribution at a deep part. A basic step of a dose calculation method is setting a dose distribution at a deep part along a central axis of a flux. Such basic dose distribution materials may be measured using a small ion chamber detector at a water phantom with scattering properties very similar to the radiation absorption of general tissue and other soft tissue. However, since it is not always possible to put a radiation detector into water, a solid drying phantom which replaces water has been developed. Polymethyl methacrylate (PMMA, Lucite, Plexiglass) and polystyrene are mostly used as dose measurement phantoms. In the case of a water phantom, dose information is obtained at each position while an ion chamber detector is moved left, right, up, and down in a phantom. In the case of a solid phantom, since it is necessary to fix a measurement point as one point and to measure while changing a thickness of the phantom, a lot of measurement time is needed and efficiency decreases a lot.
Other than a method using an ion chamber detector, there is a method of measuring a dose using optical fibers. Korean Patent Publication No. 10-2012-0085499, a prior document, discloses a method of measuring a dose of a therapeutic proton beam using optical fibers. The method of measuring the dose of the proton beam disclosed in the prior document is a technology of measuring a dose distribution of a proton beam using optical fibers with different lengths in a water phantom. To apply the technology disclosed in the prior document to detect a therapeutic proton beam emitted in a scattering mode, it is necessary to move a position of the water phantom to detect a distance through which the proton beam emitted in the scattering mode passes and a dose for each position. Accordingly, since it is necessary to move the position of the water phantom in the technology disclosed in the prior document, a long measurement time is consumed and checking an accurate position is difficult which causes a large decrease in measurement efficiency.